82 A TREATISE ON METAMORPHISM. 



It has been seen that the molecules of gases and of solids when dis- 

 solved in water are distributed through the solution. When the material 

 dissolved is not evenly distributed the molecules are more abundant here 

 and less abundant there. If the theory be true that the dissolved solids are 

 gaseous the molecules would exert a greater pressure where more closely 

 packed. Under these conditions molecules where more closely packed 

 move toward places where they are less closely packed. This move- 

 ment is regarded by many as the explanation of osmotic pressure. 

 Kahlenberg, however, does not accept this explanation, but regards osmotic 

 pressure as due to the "mutual attraction between solvent and dissolved 

 substance." 11 Without reference to either theory the more important 

 conclusions in reference to diffusion may be summarized. 



The force which drives the dissolved substances from place to place, 

 and the velocity with which a dissolved substance wanders in a solvent, is 

 proportional to the degree of concentration. 6 Therefore, "the quantity of 

 a salt which diffuses through a given area is proportional to the difference 

 between the concentrations of two areas infinitely near one another.'" 3 In 

 other words, diffusion is proportional to the difference in strength. The 

 quantity diffused is proportional to the square root of the time of diffusion, 

 and the distance over which a determinate concentration extends is also 

 proportional to the square root of the time of diffusion/ Several salts in a 

 solution diffuse almost independently of one another, each at its own specific 

 rate. e At 20°, according to Ostwald, there is twice as much diffusion as at 

 0°, and at 40° twice as much as at 20°/ When a solution is in equilibrium 

 the concentration of the solution varies inversely as the temperature. It 

 follows that when the temperature of the solution vanes, equilibrium is 

 obtained not by equal distribution of the solutes, but by unequal distri- 

 bution. If the temperature be the same throughout a solution with equal 



« Kahlenberg, Louis, The theory of electrolytic dissociation as viewed in the light of facts recently 

 ascertained: Bull. Univ. of Wisconsin No. 47, 1901, p. 349. 



&Nernst, W., Theoretical chemistry, translated by C. S. Palmer, Macmillan & Co., London, 1895, 

 pp. 143-144. 



"Ostwald, W., Solutions, translated by M. M. Pattison Muir; Longmans, Green & Co., New York, 

 1891, p. 120. 



<l Solutions, cit., p. 135. 



e Solutions, cit., p. 139. 



/Solutions, cit, p. 13C. 



